MFJ MFJ-934 User Manual

MFJ-934 Tuner/Artificial Ground Instruction Manual

MFJ-934 Antenna Tuner/Artificial Ground

P

IMPORTANT:

General Information

The MFJ-934 is a 300 watt (175 watts on 160 meters) RF output power antenna tuner and
artificial ground system that will match any transmitter or transceiver to virtually any antenna. A
special circuit in this tuner cancels the reactance of a ground lead or counterpoise, and reduces
problems caused by RF "in the shack". Forward power, reflected power, ground current, and
SWR can be read on the wattmeter's illuminated cross-needle meter.

The MFJ-934 tuner section uses a "T" network and covers all bands between 160 and 10 meters.
This network will work with dipoles, inverted-vees, verticals, mobile whips, beams, random
wires, and many other antennas. The MFJ-934 has rear panel connectors for coaxial, single wire
or two wire feedlines. A built-in 4:1 balun allows the use of balanced open wire, twinlead, or
twin-axial feedlines.

LEASE READ ENTIRE MANUAL BEFORE ATTEMPTING TO OPERATE THIS

. T

EQUIPMENT
GROUND FROM THE COUNTERPOISE TERMINAL
CONNECTED FROM THE STATION GROUND BUS TO AN ELECTRIC GROUND
LONG WIRE AND BALANCED LINE TERMINALS ON THE BACK MAY HAVE AREA

D

O NOT PLACE ANY COUNTERPOISE OR NON-COAXIAL FEED WIRES NEAR

METALLIC OR

HIS UNIT DOES NOT PROVIDE A DC OR LOW FREQUENCY EARTH

. A

SEPARATE WIRE MUST BE

RF

SENSITIVE DEVICES

.

. T

HE

.

SWR/Wattmeter and Ground Current Meter

An illuminated cross-needle meter measures the FORWARD and REFLECTED power, ground
current, and the SWR. The meter's full scale forward and reflected power range is controll ed by
the right METER RANGE switch. If your transmitter has more than 30 watts of output power,
set this switch to the 300W (button in). If your transmitter has less than 30 watts of output, use
the 30W switch position (button out).

Forward power is displayed on the left-hand FORWARD meter scale when the FORWARD
CURRENT button is out. Read directly from the scale in the 300 watt position.

In the 30W position the forward power scale must be divided by 10.

Reflected power is read on the right-hand REFLECTED meter scale. This scale indicates 60
watts full scale when the 300W power sensitivity is selected, and 6 watts when the 30W forward
power range is selected. This scale must be divided by 10 when using the 30W power range
position.

The most accurate power readings occur in the upper half of the meter scales. To accurately
measure power with a less than perfect match, the reflected power should be subtracted from the
forward power reading.

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MFJ -934 Instruction Manual
SWR is measured by observing the crossing point of the forward and reflected power needles.

No cumbersome or time consuming SWR sensitivity adjustments are required with this type of
meter. The SWR is read directly from eight red SWR curves ranging from 1:1 to infinity.
Simply observe the red SWR curve closest to where both needles cross, and read the SWR value
of the curve.

Ground current is indicated on the Forward meter scale when the FORWARD CURRENT meter
switch is depressed and locked.

Interconnections

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MFJ-934 Instruction Manual

Installation

1. Locate the tuner in a convenient location at the operating position. Avoid placing the tuner
near microphones, speech processors, computers, TNC's or other RF sensitive devices.

WARNING:

2. Install the MFJ-934 between the transmitter and antenna as shown in the interconnections
diagram. A 50 ohm coaxial cable is used to connect the transmitter to the SO-239 (UHF
female) connector labeled TRANSMITTER on the back of the tuner.

3. Connect a short heavy wire from the post labeled GROUND to the station ground bus that
connects the transmitter, receiver, and other accessories together.

4. Connect the counterpoise or RF ground to the COUNTERPOISE post. (See the Artificial
Ground operating section and the Grounding Hints section on page 6 for details of suitable
counterpoise grounds and other grounding suggestions.)

5. A coaxial feedline may be connected to the SO-239 (UHF female) connector labeled
ANTENNA.

-OR-

A random wire (longwire) antenna may be connected to the five-way binding post marked

WIRE. (See the ANTENNA HINTS section for detailed suggestions on bringing a single
wire feeder into the operating position.)

-OR-

A balanced feedline (twin lead, open wire, or twin-axial line) may be connected to the two

five-way binding posts marked BALANCED LINE. Connect an insulated jumper wire from
the WIRE binding post, as indicated by a dotted line on the MFJ-934, to one of the
BALANCED LINE posts. This connection activates the internal 4:1 balun.

Note:

Do not connect more than one antenna to the MFJ-934 at the same time, unless you want

to apply power to the antennas at the same time. If a random length wire is used, be sure
to remove the WIRE to BALANCED LINE jumper connection.

If random wire or balanced feeders are connected directly to this tuner, position
the tuner so the rear panel terminals can not be accidentally contacted by
persons or conductors. When transmitting with random wire or balanced lines,
the rear panel burns. These high RF voltages may also damage anything
contacting or within a half inch of the terminals.

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MFJ -934 Instruction Manual

Meter Lamp

The MFJ-934 has an illuminated meter. To provide power for the
meter lamp, a 12 Vdc supply such as the MFJ-1312C should be
used. Use a standard 2.5 mm coaxial plug with the center positive
and the shield ground.

Using The MFJ-934

Never Change The Antenna or Inductor Selector Switch Position While

CAUTION

In any conventional "T" network tuner, maximum power handling and smoothest tuning occur
when the capacitance in the network is as large as possible. In this tuner the TRANSMITTER
and ANTENNA controls have maximum capacitance at position 0 (fully meshed), and minimum
capacitance at position 10 (fully open). Use the highest capacitance possible (lowest number on
the front panel scale) for each band for the smoothest tuning, highest efficiency, and greatest
power handling capability. The chart in the tuning instructions shows typical capacitor settings
that can be used for each amateur band.

The INDUCTANCE switch in the MFJ-934 has maximum inductance in position "A", and
minimum inductance in position "L". The chart in the tuning instructions shows typical
INDUCTANCE switch settings for each amateur band. Less inductance is needed as the
frequency is increased. If too little inductance is used, the tuner may not match the load properly.
If too much inductance is used, the tuner will be "touchy" and power handling will be
compromised.

Most modern solid state transceivers do not require tuning and loading adjustments. If the
transceiver has a built in antenna tuner, be sure it is turned off or disabled. If your transmitter has
an adjustable output circuit, it must be properly tuned to a 50 ohm load at the operating frequency
before adjusting the tuner. This should be done with a dummy load. If you do not have a
dummy load, use the recommended maximum transmitter load setting and "dip" the plate.

Note:

Set the GROUND MATCHING controls at zero (maximum capacitance) and "L" (minimum
inductance) unless you already know the correct position for the band you are using. Ground
matching is done after the tuner is adjusted for lowest SWR.

:

Transmitting! Never Apply More Than 300 Watts To The MFJ-934.

NOT

Do
the
934 is fully tuned.

change the

tuner

has been fully adjusted. The transmitter can be "touched up" after the MFJ-

transmitter's

tuning (plate) or loading (antenna) controls until after

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